1. Field of the Invention
The invention relates generally to an electromagnetically-driven valve, and more specifically to an electromagnetically-driven valve that collectively opens and closes multiple valves provided in an internal combustion engine.
2. Description of the Related Art
For example, the specification of U.S. Pat. No. 6,467,441 describes art related to an existing electromagnetically-driven valve, more specifically, an electromagnetic actuator that actuates a valve of an internal combustion engine using electromagnetic force and elastic force of a spring in combination. The electromagnetic actuator described in the specification of U.S. Pat. No. 6,467,441 includes a valve that has a stem, and a pivot arm. The pivot arm has a first end portion that is pivotally supported by a support frame, and a second end portion that contacts a tip of the stem. Electromagnets each include a core and a coil wound around the core, and are arranged above and below the pivot arm.
The electromagnetic actuator further includes a torsion bar that is fitted to the first end portion of the pivot arm and that applies force to the valve to open the valve, and a spiral spring that is arranged around the outer periphery of the stem and that applies force to the valve to close the valve. The pivot arm is alternately attracted to the cores of the electromagnets arranged above and below the pivot arm on the basis of the elastic force of the torsion bar and the elastic force of the spiral spring.
Electromagnetically-driven valves that are structured in a fashion similar to that described above are described in Japanese Patent Application Publication No. 2007-23889 (JP-A-2007-23889), Japanese Patent Application Publication No. 2007-32436 (JP-A-2007-32436), the specification of German Patent Laid-Open Publication No. 10025491, the specification of U.S. Pat. No. 7,088,209, the specification of U.S. Pat. No. 6,571,823, and the specification of U.S. Pat. No. 6,481,396.
A structure in which two valves of an engine are collectively driven using the electromagnetically-driven valve described in each of the above documents may be employed. However, when the engine is operating at low speed or low load, a sufficient amount of air may be introduced into the engine or a sufficient amount of exhaust gas may be discharged from the engine by driving only one valve. If two valves are kept driving in such a case, the electromagnetically-driven valve may consume unnecessarily large amount of electric power.